Radio frequency (RF) filtering circuitry is critical to the operation of modern wireless communications devices. RF filtering circuitry is often used to isolate RF signals within different frequency bands from one another, allowing wireless communications devices to communicate in a number of different frequency bands (i.e., operating bands), either separately or simultaneously. FIG. 1 illustrates conventional RF filtering circuitry 10. The conventional RF filtering circuitry 10 is a diplexer including a first input/output node 12A, a second input/output node 12B, and a common node 12C. A power amplifier 14, a low noise amplifier 16, and an antenna 18 are shown for context. The power amplifier 14 is coupled between a transmit signal node 20 and the first input/output node 12A. The low noise amplifier 16 is coupled between a receive signal node 22 and the second input/output node 12B. The antenna 18 is coupled to the common node 12C.
The conventional RF filtering circuitry 10 is configured to pass RF transmit signals TX within a transmit signal frequency band from the power amplifier 14 to the antenna 18 while attenuating signals outside the transmit signal frequency band. Further, the conventional RF filtering circuitry 10 is configured to pass RF receive signals RX within a receive frequency band from the antenna 18 to the low noise amplifier 16 while attenuating signals outside the receive frequency band. In general, the RF transmit signal provided by the power amplifier 14 is a high power signal when compared to the RF receive signals RX from the antenna 18. Accordingly, it is crucial for the conventional RF filtering circuitry 10 to adequately attenuate the RF transmit signal and harmonics thereof before it reaches the low noise amplifier 16. Failing to do so may result in compression of the receive signal chain and/or leakage of intermodulation products from the transmit signal and one or more blocker signals into the receive signal path. When the conventional RF filtering circuitry 10 supports only a small number of RF frequency bands such as the diplexer shown in FIG. 1, providing adequate attenuation may be routine. However, as the number of RF frequency bands supported by the conventional RF filtering circuitry 10 increases, the ability of the circuitry to provide adequate attenuation often decreases significantly.
FIG. 2 shows conventional RF filtering circuitry 24 configured to support additional RF frequency bands. The conventional RF filtering circuitry 24 is a hexaplexer including a first input/output node 26A, a second input/output node 26B, a third input/output node 26C, a fourth input/output node 26D, a fifth input/output node 26E, a sixth input/output node 26F, and a common node 26G. A first power amplifier 28A, a second power amplifier 28B, a third power amplifier 28C, a first low noise amplifier 30A, a second low noise amplifier 30B, a third low noise amplifier 30C, and an antenna 32 are shown for context. The first power amplifier 28A is coupled between a first input/output node 34A and the first input/output node 26A. The first low noise amplifier 30A is coupled between a first second input/output node 36A and the second input/output node 26B. The second power amplifier 28B is coupled between a second input/output node 34B and the third input/output node 26C. The second low noise amplifier 30B is coupled between a second input/output node 36B and the fourth input/output node 26D. The third power amplifier 28C is coupled between a third first input/output node 34C and the fifth input/output node 26E. The third low noise amplifier 30C is coupled between a third second input/output node 36C and the sixth input/output node 26F. The antenna 32 is coupled to the common node 26G.
In operation, the conventional RF filtering circuitry 24 is configured to pass first RF transmit signals TX1 within a first transmit signal frequency band from the first power amplifier 28A to the antenna 32 while attenuating signals outside the first transmit signal frequency band, pass second RF transmit signals TX2 within a second transmit signal frequency band from the second power amplifier 28B to the antenna 32 while attenuating signals outside the second transmit signal frequency band, and pass third RF transmit signals TX3 within a third transmit signal frequency band from the third power amplifier 28C to the antenna 32 while attenuating signals outside the third transmit signal frequency band. Further, the conventional RF filtering circuitry 24 is configured to pass first RF receive signals RX1 within a first receive signal frequency band from the antenna 32 to the first low noise amplifier 30A while attenuating signals outside the first receive signal frequency band, pass second RF receive signals RX2 within a second receive signal frequency band between the antenna 32 and the second low noise amplifier 30B while attenuating signals outside the second receive signal frequency band, and pass third RF receive signals RX3 within a third receive signal frequency band between the antenna 32 and the third low noise amplifier 30C while attenuating signals outside the third receive signal frequency band.
In general, the RF transmit signals provided by the first power amplifier 28A, the second power amplifier 28B, and the third power amplifier 28C may be high power signals when compared to the RF receive signals from the antenna 32. Accordingly, it is crucial for the conventional RF filtering circuitry 24 to adequately attenuate the RF transmit signals and harmonics thereof before they reach the first low noise amplifier 30A, the second low noise amplifier 30B, and/or the third low noise amplifier 30C. Failing to do so may result in desensitization and/or damage to these low noise amplifiers, especially when one or more harmonics of the RF transmit signals fall at or near the receive signal frequency band of the particular signal path.
When the conventional RF filtering circuitry 24 supports a relatively large number of RF frequency bands such as the hexaplexer shown in FIG. 2, it may be difficult to achieve the necessary isolation in each receive signal path to prevent desensitization of the first low noise amplifier 30A, the second low noise amplifier 30B, and/or the third low noise amplifier 30C. This problem may be exacerbated in carrier aggregation schemes in which multiple RF transmit signals and/or multiple RF receive signals are simultaneously processed by the conventional RF filtering circuitry 24, as intermodulation distortion products may form due to the interaction of the various signals at the common node 26G that may be particularly difficult to attenuate. Accordingly, there is a need for improved RF filtering circuitry able to adequately attenuate undesired signals.